7.4 Groupcast mode 5G ProSe direct communication over PC5

24.5543GPPProximity-services (ProSe) in 5G System (5GS) protocol aspectsRelease 17Stage 3TS

7.4.1 Overview

This clause describes the 5G ProSe communication over PC5 reference point in groupcast mode operation. The UE is configured with the related information as described in clause 5.2.4. For commercial services, the application layer group ID is provided by application server. For public safety services, the pre-configured or provisioned application layer group ID as described in clause 5.2.4 will be used for groupcast communication.

7.4.2 Transmission of groupcast mode 5G ProSe communication over PC5

7.4.2.1 Initiation

7.4.2.1.1 Initiation of forming a group

Before the UE is requested by upper layers to send data unit(s) of a ProSe application identified by a ProSe identifier using 5G ProSe communication over PC5, for the users sharing the same application layer group ID as configured in clause 5.2.4 may perform a group member discovery procedure as specified in clause 6.2.15.

When the group is formed, the following information may be exchanged within the group members included in the application layer discovery message:

a) group size; and

b) member ID.

NOTE: Whether to transmit the application layer discovery message as metadata in a 5G ProSe direct discovery message or as user traffic over PC5 is UE implementation specific.

7.4.2.1.2 Requirements for 5G ProSe direct communication over PC5

The requirements for groupcast mode 5G ProSe direct communication over PC5 is the same as described in clause 7.3.2.1.1, with the following additions:

a) When the UE is requested by upper layers to send data unit(s) of a ProSe application identified by a ProSe identifier using 5G ProSe communication over PC5, the request from the upper layers includes:

1) the application layer group ID;

2) the group size and the member IDs;

3) the range requirement; or

4) the communication mode which is set to groupcast mode.

7.4.2.1.3 PC5 QoS flow match and establishment

The PC5 QoS flow match and establishment for groupcast mode 5G ProSe direct communication over PC5 is the same as described in clause 7.3.2.1.2, with the following modifications:

a) The UE shall determine the destination layer-2 ID as:

1) if no application layer group ID is provided by the application layer, then according to the mapping rules specified in clause 5.2.4, the UE shall set the destination layer-2 ID to the destination layer-2 ID corresponding to the ProSe identifier as specified in clause 5.2.4;

2) if application layer group ID is provided by the application layer and there is a context for the application layer group ID as specified in clause 5.2.4, then UE shall set the destination layer-2 ID to the ProSe layer-2 group ID in the context; and

3) if application layer group ID is provided by the application layer and there is no context for the application layer group ID as specified in clause 5.2.4, then the UE shall convert the application layer group ID into a destination layer-2 ID as following:

i) to use the group identifier as the input to the SHA-256 hashing algorithm as specified in ISO/IEC 10118-3:2018 [28]; and

ii) to use the 24 least significant bits of the 256 bits of the output as destination layer-2 ID; and

NOTE: SHA-256 hashing algorithm is implemented in the ME.

b) If there is no existing context for the destination layer-2 ID and optional group identifier, the UE shall proceed as:

1) to establish a new context for the destination layer-2 ID and optional group identifier;

2) self-assign a new source layer-2 ID; and

3) to pass the source/destination layer-2 IDs, optional group size and optional member IDs to lower layers.

7.4.2.2 Transmission

The transmission of groupcast mode 5G ProSe direct communication over PC5 is same as described in clause 7.3.2.2, with the following additions:

a) If group identifier is provided, then the destination layer-2 ID shall be set to the destination layer-2 ID in the context for the group identifier as specified in clause 7.4.2.1.3.

7.4.2.3 Procedure for UE to use provisioned radio resources for 5G ProSe direct communication over PC5

The procedures described in clause 7.3.2.3 apply.

7.4.2.4 Privacy of 5G ProSe direct transmission over PC5

The procedures described in clause 7.3.2.4 apply with the following additions:

a) using the privacy timer T5200 for groupcast; and

b) how to change and randomise the UE’s source layer-2 ID and source IP address including IP prefix (if used) is specified in clause 5.4 of 3GPP TS 33.536 [37] with the consideration of replacing V2X with 5G ProSe.

7.4.3 Reception of groupcast mode 5G ProSe direct communication over PC5

The reception of groupcast mode 5G ProSe direct communication over PC5 is the same as described in clause 7.3.3, with the following additions:

a) besides the configured destination layer-2 ID(s) for receiving messages over PC5, the UE shall also derive the destination layer-2 ID(s) based on group identifier(s) if provided by upper layers as specified in clause 7.4.2.1.

7.4.4 IP address allocation for groupcast mode 5G ProSe communication over PC5

When the UE needs to perform 5G ProSe communication over PC5 reference point in groupcast mode operation and the type of data in the data unit is IP, the UE uses the same IP address allocation mechanism as specified in clause 7.3.4.